The concrete pistons in concrete delivery apparatuses in contact with concrete are wearing parts and need to be replaced frequently. When the concrete delivery apparatuses are working, two concrete pistons reciprocate in a delivery cylinder one behind the other so as to continuously deliver the concrete, and when the concrete pistons need to be replaced, they must be returned back to a water tank connected with the delivery cylinder and a driving oil cylinder and then are disassembled and replaced. Thus, convenient disassembling and assembling of the concrete pistons should be taken into consideration during designing the structure of the concrete delivery apparatuses.
In existing concrete delivery apparatuses, only one concrete piston is returned back at one time, and there are three typical structures as follow:
The first one: in this structure, the concrete pistons are connected to an oil cylinder piston rod via an intermediate connection rod, and the intermediate connection rod can be connected to the concrete pistons and the oil cylinder piston rod via bolt or ferrule (see FIGS. 1 and 2). This structure comprises a delivery cylinder 101, a concrete piston assembly 102, a concrete piston connecting flange 103, an intermediate connection rod 104, a water tank 105, a left driving oil cylinder piston rod 106, (wherein the term “left” refers to the pumping cylinder structure in the upper parts of the figures) left driving oil cylinder rod chamber oil mouth 107, a left driving oil cylinder rod chamber 108, a left driving oil cylinder rod chamber oil feeding pipe 109, a left driving oil cylinder barrel 110, a left driving oil cylinder rodless chamber oil feeding pipe 111, a left driving oil cylinder piston 112, a left driving oil cylinder rodless chamber oil mouth 113, a right driving oil cylinder rodless chamber oil mouth 114, a right driving oil cylinder rodless chamber oil feeding pipe 115, a right driving oil cylinder rodless chamber 116, a right driving oil cylinder rod chamber oil feeding pipe 117, a right driving oil cylinder piston 118, a right driving oil cylinder rod chamber 119 and a right driving oil cylinder rod chamber oil mouth 20. The method and steps for replacing the concrete piston assembly 102 in the pumping mechanism as shown in FIGS. 1 and 2 are as follow: when the left driving oil cylinder concrete piston needs to be disassembled, the pressure oil of the hydraulic system enters the left driving oil cylinder rod chamber 108 through the left driving oil cylinder rod chamber oil mouth 107 and thus pushes the left driving oil cylinder piston 112 and the left driving oil cylinder piston rod 106 to retreat, the oil in the left driving oil cylinder enters the right driving oil cylinder rodless chamber 116 through the left driving oil cylinder rodless chamber oil mouth 113 and the right driving oil cylinder rodless chamber oil mouth 114 and thus pushes the right driving oil cylinder piston 118 forward, and when the left driving oil cylinder moves to the end, the intermediate connection rod 104 enters the water tank 105. Then the intermediate connection rod 104 can be disassembled, the left driving oil cylinder is operated to move the left driving oil cylinder piston rod 106 forward which then comes into contact with the concrete piston connection flange, and then a bolt is used to connect the left driving oil cylinder piston rod 106 with the concrete piston connecting flange, then the left driving oil cylinder is operated to retreat, so that the concrete piston assembly 102 returns back to the water tank and then the concrete piston assembly 102 can be replaced (as shown in FIG. 2). After the replacement is completed, the concrete piston can be restored in a reverse order. If the other concrete piston needs to be replaced, operation may be conducted in this order again. The difference lies in that the right driving oil cylinder concrete piston is operated to retreat. For this structure, only one concrete piston can be replaced at one time, and the operation takes much time and power and is of low efficiency.
The second one: as shown in FIGS. 3 and 4, the concrete pistons in this structure can be replaced and repaired more easily compared with the first structure, and in this structure a positioning sleeve is provided in the water tank between the delivery cylinder and the driving oil cylinder and is usually provided in the water tank in normal situations, thus the concrete pistons will come across the positioning sleeve when retreating and will not retreat to the water tank as it is positioned by the positioning sleeve. When the concrete pistons need to be replaced, it is only necessary to disassemble the positioning sleeve from the water tank, then the piston rod of the oil cylinder is able to further retreat a distance equal to the length of the positioning sleeve, and the concrete pistons are able to retreat to the water tank, which makes replacing the concrete pistons convenient. Compared with the first structure, the concrete pistons in this structure can be replaced more easily, but the positioning sleeve needs to be disassembled by man power during each replacement and only one concrete piston can be replaced at one time.
The third one: as shown in FIGS. 5 and 6, this structure is of high automation, the concrete pistons can be replaced and repaired very conveniently, and the piston at one side can automatically retreat to the water tank by just pressing a button. This structure is mainly achieved by providing a limit oil cylinder behind the driving oil cylinder, during normal usual operation, the limit oil cylinder is full of hydraulic oil and thus a closed chamber is formed, then the concrete pistons are not able to return back to the water tank as they are blocked by the limit oil cylinder, and when the concrete pistons need to be repaired or replaced, it is only necessary to start the button to get the oil in the limit oil cylinder back to the pressureless oil tank, then the concrete pistons will press the oil in the limit oil cylinder out when retreating and thus will further retreat a distance equal to the stroke of the limit oil cylinder, and then the concrete pistons are able to retreat to the water tank. Compared with the first and the second structures, the structure can be operated more simply and more conveniently, but it also has the shortcoming that only one concrete piston can be returned back at one time.
In conclusion, the concrete pumping structures and the control methods thereof in the prior art have problems such as low efficiency and repeated work in the regards of replacing and repairing the concrete pistons. To replace the two concrete pistons, one needs to be returned back and then the engine is shut down to release the system pressure, then the concrete piston is replaced; then the engine is started and the other concrete piston is returned back and replaced, thus the engine are started twice and shut down twice for per replacement, which takes long time and affects the construction efficiency of the concrete pump, thus improvements should be made. Especially, the two concrete pistons are used for the same period of time and have similar wear degrees, thus it would be significant to the replacement efficiency if they can be replaced at the same time.